Often it is necessary to be able to measure the strength properties of materials. For example, in the fabrication of rubberized asphalt, the selection of the type and amount of rubbery material to be used in the asphalt will alter various strength properties of the asphalt, for example, the force required to pull the asphalt mass apart and the persistence of this force. These properties are related to toughness and tenacity (described below).
Asphalt, because of its availability, low cost, and ease of handling is a valuable base material for a wide variety of uses ranging from asphaltic concrete paving, sealants and adhesives to roofing and pond membranes, mastics and coatings. Although quite versatile in its application areas, it is, nevertheless, deficient in certain performance properties such as flexibility at low temperatures and toughness at elevated temperatures. To improve these properties as well as impart additional flexibility, elasticity, water resistance, etc., certain thermoplastic type polymeric modifying materials such as synthetic rubber have been added to the base asphalt. Often these materials are added in the range of 0.5 to 10 weight percent of the base asphalt. The selection of the exact rubbery material to be used to obtain the desired properties for a particular application is one that requires very carefully controlled laboratory tests and examinations.
When selected rubbery materials and asphalt are combined, nearly every important physical property of the asphalt is altered to some degree. The most prominent effect to be noted is the force required to pull apart masses of rubberized asphalt and particularly, the persistence of this force over long extensions.
A simple test, referred to as the Benson Test Method, has been used to measure these properties in asphalt but its usefulness is limited by the adhesive bond strength between the test measuring apparatus and the asphalt. In making the test, a small (1.905 cm, 0.75 in diameter) hemispherical metal head is lowered into a molten sample of asphalt to be tested, the head being lowered sufficiently to bring substantially the entire hemispherical surface in contact with the sample but not so far that the asphalt covers the head. The sample is then cooled to a desired temperature, and the force required to remove the head is recorded. The Benson Test Method is described in Roads and Streets, April 1955, pg. 138 and Roads and Engineering Construction, August 1955, pg. 78. The test, however, is limited to asphalt compositions containing less than about 2 or 3 weight percent rubber because at about that point, the cohesive strength of the asphaltic composition begins to exceed its adhesion to the metal head. Hence, there exists a need for some type apparatus or test method to accurately measure toughness and tenacity of asphaltic compositions containing more than about 2 or 3 weight percent rubber.
It is an object of this invention to measure strength properties of various materials. Another object of this invention is to provide a test apparatus for such measurement.